1. Field of the Invention
The present invention relates generally to a molded packaging tray used in packaging meat and poultry with a stretch film overwrap and particularly to such a tray adapted for use in an "In-Line" packaging machine.
2. Description of the Related Art.
Stretch-film wrapping machines are typically used to package meat and poultry by film wrapping the poultry on trays fed sequentially to the machine. The trays used in such operations are typically molded of a polystyrene foam material and assume a substantially rigid form with limited flexibility.
There are two types of stretch film wrapping machines used with polystyrene trays. One such machine is referred to as the Push-Through type machine and the other machine is referred to as an "In-Line" type machine and which represents a more recent development in the trade.
The Push-Through machine secures a precut rectangular piece of film over an aperture. A loaded tray is then pushed vertically upward through the aperture and into the secured film. Since the film is stationary in relation to the loaded tray moving through it, the film is stretched over the product and tray. This stretching action applies as a downward force vector on the outer edge or lip of the tray. Accordingly, for the Push-Through machine, the lip of the tray is designed, for example, as illustrated in FIG. 1 and is engineered primarily to counter this downward force vector. Other trays of somewhat different cross-section for use in the Push-Through machine and adapted to counter this downward force vector are also known. The lip is typically round and thin and typically does not permit flat side sealing.
By comparison, the "In-Line" machine forms a continuous tube around a queued assembly of loaded trays flowing in a substantially horizontal path into the machine. As the tube of film surrounds each tray, the film is stretched over the lip as on the Push-Through machine. The stretching action applies a downward force vector to the lip of the tray. However, unlike the Push-Through machine, the "In-Line" machine uses a different system for cutting and folding of the film tube to produce individual packages. During this process, it is necessary that the film wrapped tray be held firmly. To accomplish this, the package is sandwiched and slightly compressed between opposed/vertical surfaces of two parallel transport belts which move the tray in a generally horizontal path. The cutting of the "tube", folding of the ends and tucking of the remaining film are accomplished while the tray is sandwiched between the vertical surfaces of the transport belts. If sufficient squeeze pressure is not applied to a tray during the aforementioned operations, the tray will slip in the transport belt causing loss of tray/machine registration, miswrapped packages, machine damage and machine down time. Therefore, sufficient squeeze pressure must be applied to avoid tray slip in the transport belts. Representative examples of an "In-Line" machine include Weldotron models 2002 and 2004, manufactured by Omori of Tokyo, Japan.
Prior to the present invention, it has been the practice to use the Push-Through type trays in the "In-Line" machine. However, the conventional Push-Through machine tray has proven to be inadequate to prevent slip and when used on the "In-Line" stretch wrap machine tends to cause loss of tray/machine registration, breakage of trays by end wall and sidewall fracture, miswrapped packages, machine damage and machine down time. Because of the increasing use of "In-Line" machines for large volume packaging, the poultry industry has encountered a problem of considerable magnitude.
The primary object of the invention thus becomes that of providing an improved poultry tray suited to use in the "In-Line" machine without encountering the various described problems. Other objects will become apparent as the description proceeds.